PHOTOPRODUCTION OF VOLATILE ORGANIC COMPOUNDS FROM SECONDARY ORGANIC AEROSOLS: AN UNEXPLAINED SOURCE? Kurtis Malecha Nizkorodov Group September 4,

INTRODUCTION TO ATMOSPHERIC AEROSOLS 2 VOCs O 3,OH,NO 3 Seed Particle SOA POA VOCs = Volatile Organic Compounds SOA = Secondary Organic Aerosol POA = Primary Organic Aerosol SOA (Condensed Phase) hνhν VOCs Historical Assumption: formation and ageing of SOA exclusively in gas-phase 2 Emerging results: condensed-phase SOA photochemistry is important! 3 VOC Production – e.g., Formic Acid 2.Hallquist, M. et al. ACP, (2009). 3.Nguyen, T. et al. ACP, (2014). Historical Assumption: formation and ageing of SOA exclusively in gas-phase 2 Emerging results: condensed-phase SOA photochemistry is important! 3 VOC Production – e.g., Formic Acid 2.Hallquist, M. et al. ACP, (2009). 3.Nguyen, T. et al. ACP, (2014). 1.IPCC, 2007

FORMIC ACID Formic Acid present in atmosphere Global Production – up to 120 Teragrams Carbon/year 4 ~27 Tg C/year is from oxidation of Organic Aerosols 4 Contributes to acid rain in remote environments 5 Variety of sources exist: 6 Direct: Anthropogenic and Biogenic Exhaust, Vegetation, Forests, Biomass Combustion Indirect: Photooxidation of monoterpenes, Ozonolysis of alkenes 3 4.Stavrakou, T et al. Nature geoscience (2012). 5.Chameides, W. & Davis, D. Nature (1983). 6.Finlayson-Pitts, B., Pitts, J. Chemistry of the Upper and Lower Atmosphere (2000).

GOALS AND MOTIVATIONS Climate models underpredict HCOOH by up to 90 Tg C/year 6 Nature, 2012 – lack of laboratory experiments for formic acid production using monoterpenes and isoprene Large unidentified secondary biogenic source? Goal: test production rate of VOCs from condensed-phase SOA photolysis Initially: use Cavity Ring Down Spectroscopy (CRDS) for detection 4

CAVITY RING DOWN SPECTROSCOPY  = cavity ring down time with analyte;  0 = empty cavity ring down time c = speed of light  = absorption coefficient R = mirror reflectivity; L = cavity length 5 0 Image adapted from: Wojtas, J. et al. Sensors (2013). Equations adapted from: Berden, G. Cavity Ring Down Spectroscopy (2009).

METHODS USED 1.Nd:YAG pulsed laser 2.Optical Parametric Oscillator/Optical Parametric Amplifier (OPO/OPA) – IR Beam 3.Cavity with highly-reflective mirrors (>99.95%)

SPECIFIC SUMMER GOALS “Rebirth” the laser and associated components of the CRDS Fix the laser Begin scans of known compounds 7

MY INITIAL SUMMER WORK Computer controlling CRDS instrument was nonfunctional Extracted data and programs Replaced computer and reloaded everything Optics in OPO were misaligned Aligned them Mirror mount adjustments were not reproducible Ordered new mounts Research with lasers is slow-going initially with a steep learning curve. 8

EXPERIMENTAL SETUP 9 Image credit: Sergey Nizkorodov

BACK TO THE LASER… Laser was not seeding properly Consequence – unable to resolve ro-vibrational lines of CO Aligned seeder spatially Better scan, but Signal:Noise is poor Aligning a seeder beam takes awhile. 10

ABSORBANCE OF CO The mirrors are not as good as they used to be. 11

SUMMARY AND ACKNOWLEDGEMENTS Condensed-phase SOA photolysis for production of Formic Acid? Using CRDS for monitoring This summer: Fixed Laser Replaced Computer Began scans of molecules Future: Obtain new mirrors Perform scans of Methane Begin making SOA for photolysis Thanks to: Nizkorodov Group Funding: NSF AGS , Photochemistry in Organic Aerosols 12